How to find what is using port 3000 on a Mac

Open the notch, choose Disk, then Monitor, and switch to Ports. Type 3000 in the filter. If something is listening there, you see its project folder, its command line and its working directory. You can open it in a browser, show the folder in Finder or ask it to quit, without writing an lsof command.

Steps

1. Open the notch and choose Disk.
2. Choose the Monitor section, then press Ports. The other view is Usage.
3. The count at the top reads like “5 listening, 3 local”.
4. Type the port in the filter field, for example 3000. It matches the port number, process, project, command and working directory, so you can also type a project name.
5. Read the row. It shows the port in bold, the project name, the command line (for example the dev server script), and the folder path with your home folder shortened to a tilde.
6. The tag on the right says local if the address is only reachable from this Mac, or network in orange if other machines can reach it.

What you can do from the row

• Open in browser goes to http://localhost and the port.
• Show project in Finder reveals the working directory. It is disabled when no folder is known.
• Stop asks the process to quit. See stopping a dev server for how that works.

How it gets the data

NotchStar reads the system’s own lsof and ps. The Ports list refreshes about every nine seconds while the Monitor section is on screen, and sampling stops when you leave. It does not run in the background.

Limits

• TCP listeners only. UDP sockets and outgoing connections are not listed.
• Your processes are the ones you can stop. macOS refuses to let you stop other users’ processes, and NotchStar does not ask for extra privileges.
• The project name is a guess. It is the nearest folder above the working directory that looks like a project, or the directory itself.
• A process started in a container may show as the container runtime rather than your server.
• It is not a firewall or a security scanner. The network tag tells you the listening address, not whether a firewall blocks access.
• Sample lag. A server that started a moment ago may take a refresh to appear.

If the Ports list is empty, the filter may be hiding everything, or nothing is listening. The tab says “No port matches” or “Nothing is listening on a port.” Pair this with the CPU view when the port is held by something busy. The Disk page lists the other seven sections.